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Camshafts


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Guest Nismo_Freak

What kind of gains are seen from a bump in duration and lift?

RB26DETT

Say using the 272 duration / 10.5mm lift, w/ valve springs on a fairly standard motor using only intake, 12 psi boost, full turbo back exhaust, fmic, and a HKS AVC (the fuel controller).

I would also swap the cam gears for adjustables and go with a 4 degree retard on the exhaust with a 1 degree advance on the intake.

Assuming fuel was optimized for the added airflow and tuned properly.

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The gains are huge, it will be one of the most important factors in getting huge horsepower. Without decent cams then the potential of any turbo is not used. I would only tend to use cams like that with a bigger turbo, but even without it a 10-15% increase in power is possible.

See'ya:burnout:

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Guest Nismo_Freak

Sounds about right I suppose... the camshafts only increase the efficiency of the motor at the higher revolutions with a slight drop at lower rpms. This in turn creates lag as noted. But the end result is more power produced at lower boost levels. The requirement for octane however goes up because the dynamic compression increases, the same when boosting more. I just needed some numbers to go by. The stock cams are as follows, I believe:

Intake: 240 duration w/ .338 lift (8.58mm)

Exhaust: 236 duration w/ .326 lift (8.28mm)

The use of the cam gears will allow me to maintain the midrange and gain back some of the boost threashold lost when I moved to the hotter cams.

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The 272's will kick in at around 4000+rpm and give the motor more legs to 8000+rpm. Something around 250 or so duration would be a better choice for a streeter. I think there are a few around 254 duration.

Most aftermaket cams need to 'dialed in' according to the motor. The factory usually designs them for a 0 deg fit but, depending on what you have done they may benifit with various timing settings.ie: don't take 4 degrees as gospel if you use non factory cams.

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